Mitsubishi MELSEC QJ71C24, User Manual

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MELSEC-Q
11 TROUBLESHOOTING
11.3.11 Communication error "SIO"
Symptom Cause Corrective action MC
Bidirectional
N
on
procedure
Pre-defined
• Data does not match the
stop bit setting.
• Check if the Q series C24 and external device
settings are the same.
• Transmission rate is too
fast and the next data is
transmitted before the Q
series C24 completes
processing of the receive
data.
• Decrease the transmission rate and restart
data communications.
• Data larger than the
receive buffer size was
received.
• Use DTR and DC control and interrupt
transmission before the buffer becomes full.
Perform RS and CS control when the modem
function is used.
• Increase the transmission interval and provide
an ample programmable controller CPU read
processing time.
Note
• The non procedure protocol stores the data
received up to first the end code received,
or fixed length data, to the non procedure
receive buffer memory and turns on the
Read Request signal to the programmable
controller CPU.
If the next data is sent while the Read
Request signal is ON, the data is
temporarily stored to the OS receive buffer.
When the OS receive buffer becomes full,
the Q series C24 skips the rest of the data
and turns on the "SIO" LED.
• Communication
error signal "SIO"
turned on.
• With a multidrop link, two
or more devices
transmitted data at the
same time.
• Connect the external devices and the Q series
C24 in a 1:1 configuration and perform a
communications test. Since data is
transmitted simultaneously from two or more
devices with a multidrop link when normal
communications among all the devices is
possible, interlock the devices so that cannot
transmit simultaneously.